Relationship between photocatalytic activity, hydrophilicity and self-cleaning effect of TiO2/SiO2 films

Self-cleaning glass can be realized utilizing photo-induced hydrophilicity of titanium dioxide. In order to under-stand the photo-induced hydrophilic self-cleaning effect, it is necessary to understand the relationship between the mutual effect of photohydrophlicity and photocatalysis. In this paper, the relationship between hydrophilicity, photocatalysis and the self-cleaning effect is investigated. It is found that the TiO2/SiO2 surface can have more hydrophilic activity and less photocatalytic activity, or vice versa by adding different amount of SiO2. It is the synergetic effect of hydrophilicity and photocatalysis that improves and maintains the self-cleaning effect. SiO2 addition increases the acidity which results in the increase of the hydroxyl content in the composite films. with the consequence that the hydrophicity and photocatalytic activity are increased during UV irradiation thus enhances the self-cleaning effect. (C) 2004 Elsevier B.V. All rights reserved.